The invention relates to an electrical contact pin for mounting in a through hole in a printed circuit board, which contact pin has a pointed part and a longitudinal contact part which interacts with the hole when mounted therein, and the cross-section of which in general has an H-shape formed through four fins which project parallel to the longitudinal axis of the pin and are connected over the longitudinal distance of the contact part by a central cross rib and define two longitudinal recesses situated on either side of the cross rib, each longitudinal recess having an essentially V-shaped floor. U.S. Pat. No. 4,728,164, granted Mar. 1, 1988 and assigned to applicants' assignee discloses such a contact. Such pins, also known as press-fit pins, are mounted in through holes of printed circuit boards. The holes are provided with a metallization, generally consisting of copper, possibly with a thin layer of tin over it. In such an electrical connection between pin and metallization no solder or similar bonding is required any more, but the electrical contact is obtained by the close form-fit and frictional connection.
In practice, such pins are virtually entirely made of square wire or flat strip material, the longitudinal recesses of the contact part being formed by stamping technology, and the fins being forced or extruded outwards, upwards or downwards. In the case of the pin known from the above-mentioned U.S. Patent the object is that the four fins on insertion of the pin into the hole of the printed circuit board should be bent inwards gradually, so that a four-point fixing in the hole is obtained. The H-shaped design means that the risk of the pin turning during mounting is reduced or ruled out. Consequently, as stated above, square pins of the type widely used in the printed circuit board industry can be used. It is very important here that the projecting fins are constructed absolutely symmetrical and have the same thickness, so that when they are being inserted in the hole all four bend over uniformly and engage the metallization in the hole. For, slight differences in thickness and therefore in stiffness of the projecting fins lead to rotation or excentric positioning of the pin being obtained during insertion, and this can cause serious damage to the metallization in the hole. It can also give rise to more wear in the counter plug present on the rear side of the printed circuit board, through the fact that the rotated square pin then has sharper engaging faces with the fixed counter plug.
In the case of the pin known from the above-mentioned U.S. Patent the flat floors have a V-shape on either side of the cross rib in the longitudinal recesses. The longitudinal recesses with the V-shaped floors are obtained by means of corresponding knife-shaped dies. During this stamping of the longitudinal recess this V-shaped floor acts as a centering facility, so that an absolutely symmetrical design of the fins on either side of the recess with the same thickness and height is obtained.
It has now been found in practice in the case of contact pins, and in particular when their dimensions are very small, that the deformations caused to the hole metallization still exceed those set in the standards. The deformation in the hole metallization is then e.g. greater than the requirement of 0.05 mm of the MIL standard. The transition present in the fin height in the known contact pin from the right pointed part to the contact part, which transition is curved inward slightly, has been found completely inadequate in practice to prevent such deformations.